1. Field of the Invention
The present invention relates to an apparatus and method for controlling power in a mobile communication system; and, more particularly, to a power control apparatus and method for a mobile communication system, which can efficiently perform a power control even when there is an abrupt change in a wireless channel environment that occurs while a mobile communication terminal moves at high speed, by allowing a terminal to request a base station to adjust Channel Quality Indicator (CQI) report frequency based on its own moving speed, and allowing, in response to such request for CQI report frequency adjustment from the terminal, the bases station to determine an optimal CQI report frequency using a downlink data transmission rate and an uplink data transmission rate of the terminal.
This work was supported by the IT R&D program of MIC/IITA [2005-S-404-13, “Research & Development of Radio Transmission Technology for 3G evolution”].
2. Description of Related Art
In conventional mobile communication systems, a power control method is generally carried out as follows.
First, when a terminal measures CQI every a k-number of subframes and then reports it to a base station, the base station extracts a Signal to Interference Ratio (SIR) from the CQI reported from the terminal.
Next, the base station calculates a downlink output power based on the extracted SIR and then adds a certain margin set in consideration of errors in measurement and calculation to the calculated output power to finally calculate a downlink output power.
Thereafter, for stability of output power, the base station obtains an average value of CQIs for an M-number of subframes which is larger than or equal to a k-number of subframes corresponding to a CQI report frequency to determine a stable downlink output power.
Hereinafter, an example frame structure of an uplink High Speed-Dedicated Physical Control Channel (HS-DPCCH) will be described with reference to FIG. 1.
As shown in FIG. 1, the uplink HS-DPCCH transmits an uplink feedback signaling associated with downlink High Speed-Downlink Shared Channel (HS-DSCH) data transmission. The feedback signaling consists of Acknowledgement (ACK)/Negative ACK (NACK) information for composite Automatic Repeat Request (ARQ) and CQI.
An HS-DPCCH frame is divided into 5 subframes with length of 2 ms, each of which is composed of 3 slots. The ACK/NACK information for composite ARQ is sent into a first slot of each subframe and CQI is sent into second and third slots of each subframe. HS-DPCCH is always sent along with an uplink DPCCH.
CQI permits a mobile station to transfer status information of downward wireless channel obtained from measurement of downlink Common Pilot Channel (CPICH) or Transport Format and Resource Indicator (TFRI) value calculated from the status information to a bases station. And, ACK/NACK serves to inform ACK or NACK information on transmission of user data packet to downlink HS-DSCH by a hybrid ARQ mechanism.
In the above-discussed conventional method, however, when a terminal reporting CQI every a k-number of predetermined subframes moves at high speed, there may be a large channel change that occurs between reports of CQI. Because of this, a transmission power determined by CQIs previously reported is not suitable for a next output signal, which results in a loss of packets.